Associated with recent miniaturization of electric appliances, miniaturization of a substrate with semiconductor chips mounted thereon is required. To mount semiconductor chips on the substrate, adhesive films are used. As a silicone wafer is getting thinner, an adhesive film is desired which can be pressure bonded at a lower temperature with a lower pressure to prevent the wafer from warping, cracking during the pressure bonding, or to prevent a substrate from cracking when the chip is thermocompression bonded to the substrate.
In Ball Grid Array (BGA) package, a semiconductor chip is adhered to a wiring board made from resin and then encapsulated with a molding compound. The wiring board has a wiring pattern and spaces between the patterned wiring tend to remain as voids in cured adhesive. To prevent voids from occurring, melt viscosity of the adhesive may be lowered. However, in a streamlined process where the adhesive is not cured in chip mounting process but cured in the encapsulation process and thinner encapsulation is employed, chips on the molten adhesive may be shifted or dislocated. Thus, an adhesive film is desired which can be pressure bonded at low temperature and at low pressure and has appropriate minimum melt viscosity.
Meanwhile, a semiconductor device is generally prepared by the following processes:
i) fixing a large-diameter silicon wafer on a pressure sensitive tape called dicing tape,
ii) dicing the wafer,
iii) picking up the diced chip from the dicing tape, and
iv) thermocompression bonding the picked up chip on a lead flame using curable liquid adhesive, i.e., die bonding adhesive.
Recently, a tape or sheet used both in the dicing and the die bonding processes, hereinafter referred to as dicing and die bonding tape, has been developed. In the dicing process, the tape is used to fix a silicon wafer, preventing diced chips from flying off. The diced chip is picked up with an adhesive layer of the tape attached on its bottom surface and then the chip is bonded to a lead flame via the adhesive layer which is then cured. The adhesive layer of this tape, too, needs to be improved in the aforesaid points.
As an adhesive, heat resistant siloxane-modified polyimide or polyamideimide has been proposed in Japanese Patent Applications Laid-Open No.3-189127 and No.4-264003. These resins, however, do not show satisfactory adhesion strength or heat resistance.
Japanese Patent Application Laid-Open No.10-60111 discloses a siloxane-modified polyamideimide having two or more of maleimide groups. The siloxane-modified polyamideimide improved properties at high temperature but has low adhesion to a copper foil.
Japanese Patent Applications Laid-Open No.7-224259 and No.8-27427 disclose heat resistant adhesive film comprising a polyimidesilicone and an epoxy resin. The polyimidesilicone does not have curable functional groups and consequently adhesion strength and reliability of the adhesion are not good.
Japanese Patent No.3221756 discloses a heat resistant adhesive film comprising a polyimidesilicone having phenolic hydroxide groups and an epoxy resin. The adhesive film is not satisfactory in bonding property at a low temperature and a low pressure and voids or shifted chips are observed.
Japanese Patent Application Laid-Open No.9-67558 discloses a dicing and die bonding tape comprising a thermoplastic polyimide layer formed on a plastic film substrate. The polyimide layer is thermocompression bonded to a silicon wafer so strongly that picking up of diced chips is not easy. Further, adhesion strength, particularly adhesion strength after exposed to humid or at a high temperature required in wire-bonding, encapsulation, and solder reflow processes, of the thermoplastic polyimide is not strong due to the thermoplasticity.
Japanese Patent Application Laid-Open No.2002-256236 and Japanese Patent No.2984549 disclose a dicing and die bonding tape comprising a resin layer composed of (A) polyimide resin, (B) epoxy resin, (C)phenolic resin, and (D)curing promoter which is formed on a film substrate. The die bonding layer of the tape comprises a curable epoxy resin to show a strong adhesion strength even after being exposed to humid or high temperature.
However, picking up of diced chips tends to be difficult to control with the aforesaid dicing and die bonding tape. A reason for this is considered to be as follows: A pressure sensitive adhesive layer of the tape is made from a radiation polymerizable composition comprising (meth)acrylate copolymer, a polymer having (meth)acryl groups or multifunctional acrylic compounds, and a photoinitiator; These components are miscible with the epoxy rein and tends to adhere strongly to the epoxy resin in UV-ray polymerization reaction process or to the softened epoxy resin in thermocompression bonding in the dicing process. The pressure sensitive adhesion strength of the pressure sensitive adhesive layer to the die bonding layer tends to change with time, which makes the picking up of the diced chips more difficult.